In Situ Manipulation and Micromechanical Characterization of Diatom Frustule Constituents Using Focused Ion Beam Scanning Electron Microscopy

Biocomposite structures are difficult to characterize by bulk approaches due to their morphological complexity and compositional heterogeneity. Therefore, a versatile method is required to assess, for example, the mechanical properties of geometrically simple parts of biocomposites at the relevant length scales. Here, it is demonstrated how a combination of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and micromanipulators can be used to isolate, transfer, and determine the mechanical properties of frustule constituents of diatom Thalassiosira pseudonana (T.p.). Specifically, two parts of the diatom frustule, girdle bands and valves, are separated by FIB milling and manipulated using a sharp tungsten tip without compromising their physical or chemical integrity. In situ mechanical studies on isolated girdle bands combined with Finite Element Method (FEM) simulations, enables the quantitative assessment of the Young's modulus of this biosilica; E = 40.0 GPa. In addition, the mechanical strength of isolated valves could be measured by transferring and mounting them on top of premilled holes in the sample support. This approach may be extended to any hierarchical biocomposite material, regardless of its chemical composition, to isolate, transfer, and investigate the mechanical properties of selected constituents or specific regions.

Modifying the thickness, pore size, and composition of diatom frustule in Pinnularia sp. with Al3+ ions

Diatoms are unicellular photosynthetic algae that produce a silica exoskeleton (frustule) which exposes a highly ordered nano to micro scale morphology. In recent years there has been a growing interest in modifying diatom frustules for technological applications. This is achieved by adding non-essential metals to the growth medium of diatoms which in turn modifies morphology, composition, and resulting properties of the frustule. Here, we investigate the frustule formation in diatom Pinnularia sp., including changes to overall morphology, silica thickness, and composition, in the presence of Al³⁺ ions at different concentrations. Our results show that in the presence of Al³⁺ the total silica uptake from the growth medium increases, although a decrease in the growth rate is observed. This leads to a higher inorganic content per diatom resulting in a decreased pore diameter and a thicker frustule as evidenced by electron microscopy. Furthermore, ²⁷Al solid-state NMR, FIB-SEM, and EDS results confirm that Al³⁺ becomes incorporated into the frustule during the silicification process, thus, improving hydrolysis resistance. This approach may be extended to a broad range of elements and diatom species towards the scalable production of silica materials with tunable hierarchical morphology and chemical composition.

In Situ Observation of Nanoparticle Exsolution from Perovskite Oxides: From Atomic Scale Mechanistic Insight to Nanostructure Tailoring

Understanding and controlling the formation of nanoparticles at the surface of functional oxide supports is critical for tuning activity and stability for catalytic and energy conversion applications. Here, we use a latest generation environmental transmission electron microscope to follow the exsolution of individual nanoparticles at the surface of perovskite oxides, with ultrahigh spatial and temporal resolution. Qualitative and quantitative analysis of the data reveals the atomic scale processes that underpin the formation of the socketed, strain-inducing interface that confers exsolved particles their exceptional stability and reactivity. This insight also enabled us to discover that the shape of exsolved particles can be controlled by changing the atmosphere in which exsolution is carried out, and additionally, this could also produce intriguing heterostructures consisting of metal-metal oxide coupled nanoparticles. Our results not only provide insight into the in situ formation of nanoparticles but also demonstrate the tailoring of nanostructures and nanointerfaces.

In situ stabilizer formation from methacrylic acid macromonomers in emulsion polymerization

Methacrylic acid oligomers containing a propenyl ω-endgroup were synthesized by CCTP and used as precursors to efficient stabilizers in surfactant-free emulsion polymerization.

In situ compatibilisation of alkenyl-terminated polymer blends using cross metathesis

A whiff of diblocks is enough! Straightforward coupling of two vinyl-terminated macromolecules was achieved by cross metathesis (CM) using Grubbs' second-generation catalyst (G2) giving access to a diversity of “self-compatibilised” polymer blends. Solution blends, in the absence of G2, showed clear macrophase separation while metathesized samples no longer did. A small fraction of diblocks only proved to act as an excellent compatibilizer.